The present invention is directed to inks, such as hot-melt ink compositions containing a colorant, and a vehicle, and more specifically, the present invention relates to hot melt inks with, for example, a controlled morphology, a melting point of, for example, from about 25.degree. C. to about 150.degree. C., and preferably from about 30.degree. C. to about 100.degree. C., and which inks are especially useful for acoustic ink printing processes and apparatuses, reference, for example, U.S. Pat. Nos. 5,121,141, 5,111,220, 5,128,726, 5,371,531, the disclosures of which are totally incorporated herein by reference, including especially acoustic ink processes as illustrated in a number of the aforementioned copending applications and patents, such as an acoustic ink printer for printing images on a record medium.
More specifically, the inks of the present invention are comprised of a colorant such as a dye or a pigment, and a vehicle comprised of a mixture of an alkane, such as an alkylene wax, and a crystallinity and spherulite growth inhibitor, such as an oxazoline, or an oxazoline available from Angus Chemical, like Alkaterge T, Alkaterge E, plasticizers, and/or nucleating agents, such as those described in U.S. Pat. No. 5,275,903, the disclosure of which is totally incorporated herein by reference. The alkane components preferably of a waxy nature are selected for the hot melt formulations, and these components are preferably crystalline or semicrystalline in the solid state. When solidified on a substrate, such as paper or a transparency, the alkanes, especially higher carbon chain alkanes with, for example, 14 or more carbons, and up to, for example, 1,000 carbon atoms, crystallize in a spherulitic morphology. It can be of importance to control the size of the spherulites to be, for example, between about 0.1 and about 10 microns, and preferably between about 1 and about 4 microns, primarily to enable optimum projection efficiency and excellent crease resistance, and wherein the opacity increases with the size of the spherulites. The spherulite size can be measured by an optical microscope with cross polarized light or by the low angle solid state light scattering method (R. S. Stein and M. B. Rhodes, J. Appl. Phys., 31, 1873 (1960). Large spherulites of size greater than, for example, about 5 microns could result in brittle prints. It is a purpose of the present invention to control the size of the spherulites by formulating binary or ternary blends of waxes, oxazolines and nucleating agents. Furthermore, this invention relates to inks with additives, such as oxazolines, that when solidified form a dispersed phase of small spherulitic crystalline domains in the matrix of a wax, or vice versa.
With the inks of the present invention there can be generated excellent developed images on plain and coated papers with acceptable image permanence, excellent projection efficiency on transparencies without needing a post fusing step, and excellent crease resistance, and wherein the inks possess acceptable, and in embodiments superior lightfastness, and superior waterfastness. Moreover, in embodiments of the present invention there is enabled the elimination, or minimization of undesirable paper curl since water need not be present in the invention inks, and it is preferred that there be an absence of water, thus a dryer can be avoided thereby minimizing the cost of the acoustic ink jet apparatus and process. Furthermore, with the present invention in embodiments there are enabled inks with a low viscosity of, for example, from about 1 centipoise to about 10 centipoise at a temperature of, for example, from about 40.degree. C. to about 160.degree. C., and preferably from about 40.degree. C. to about 125.degree. C. as measured by Carri-Med CSL-100 rheometer TA Instrument, and which inks can be utilized at low jetting temperatures with an acoustic printing device, for example low temperatures of less than about 170.degree. C., and more specifically, from about 50.degree. C. to about 160.degree. C.